1. Field of the Invention
The present invention relates to a marine vessel propulsion apparatus.
2. Description of the Related Art
An outboard motor is an example of a marine vessel propulsion apparatus included in a marine vessel. A conventional outboard motor is described, for example, in U.S. Patent Application Publication No. 2008/0268726. The outboard motor includes an engine arranged to rotate a propeller, and an ECU (electronic control unit) arranged and programmed to control the outboard motor. The ECU drives the marine vessel forward and in reverse by making the engine rotate a propeller. The engine includes a crankshaft arranged to be capable of rotating, a camshaft arranged to rotate in linkage with the rotation of the crankshaft, a magnetic sensor arranged to detect a rotation angle of the crankshaft, and a magnetic sensor arranged to detect a rotation angle of the camshaft.
The engine rotates the crankshaft in one rotation direction to rotate the propeller. A rotation direction of the propeller is switched according to a shift position of the outboard motor. When the marine vessel is being driven forward in a normal state, the propeller rotates forward. When the marine vessel is being driven in reverse in a normal state, the propeller rotates in reverse. The crankshaft rotates in only the one direction and the rotation direction of the propeller is switched by switching a dog clutch provided between the crankshaft and a propeller shaft. However, when the shift position of the outboard motor is switched from a forward drive position to a reverse drive position in a state where the marine vessel is being driven forward at high speed, the crankshaft may rotate in reverse.
Specifically, immediately after the shift position of the outboardmotor is switched from the forward drive position to the reverse drive position in the state where the marine vessel is being driven forward at high speed, the marine vessel is driven forward by inertia and thus a resistance (water pressure) that makes the propeller rotate forward is applied to the propeller. The resistance is transmitted to the crankshaft. The shift position of the outboard motor at this point is the reverse drive position and thus the resistance that makes the propeller rotate forward is transmitted to the crankshaft as a force that makes the crankshaft rotate in reverse. The crankshaft may thus rotate in reverse when the shift position of the outboard motor is switched from the forward drive position to the reverse drive position in the state where the marine vessel is being driven forward at high speed.
When the crankshaft rotates in reverse, an interior of an exhaust passage connected to an exhaust port of the engine is put in a negative pressure state, and thus water, which is present outside the outboard motor and is sucked into the exhaust passage through an exit of the exhaust passage that opens at the propeller, may enter into an interior of the engine. Also, when the crankshaft rotates in reverse, a relationship between a rotation period of the crankshaft and a rotation period of the camshaft changes. In U.S. Patent Application Publication No. 2008/0268726, the ECU detects the reverse rotation of the crankshaft based on this relationship.